Voltage regulator

ABSTRACT

One example discloses a voltage regulator, including: a power supply input; a regulated voltage output; an output transistor coupled to the power supply input and the regulated voltage output; and a current amplifier coupled between the power supply input and the regulated voltage output; wherein the current amplifier is configured to supply a second current from the power supply input to the regulated voltage output when a first current between the power supply input and the output transistor exceeds a threshold current.

The present specification relates to systems, methods, apparatuses,devices, articles of manufacture and instructions for voltageregulation.

SUMMARY

According to an example embodiment, a voltage regulator, comprising: apower supply input; a regulated voltage output; an output transistorcoupled to the power supply input and the regulated voltage output; anda current amplifier coupled between the power supply input and theregulated voltage output; wherein the current amplifier is configured tosupply a second current from the power supply input to the regulatedvoltage output when a first current between the power supply input andthe output transistor exceeds a threshold current.

In another example embodiment, the output transistor is an NMOStransistor having a drain coupled to the power supply input and a sourcecoupled to the regulated voltage output.

In another example embodiment, the second current supplied by thecurrent amplifier to the regulated voltage output is a multiple of thefirst current between the power supply input and the output transistor.

In another example embodiment, the current amplifier includes anamplifier control circuit and an amplified current circuit; theamplifier control circuit, is coupled between the power supply input andthe output transistor, and is configured to sense the first currentbetween the power supply input and the output transistor; and theamplified current circuit, is coupled to the amplifier control circuit,and is coupled between the power supply input and the regulated voltageoutput, and is configured to supply the second current from the powersupply input to the regulated voltage output when the first currentbetween the power supply input and the output transistor exceeds thethreshold current.

In another example embodiment, the amplifier control circuit and theamplified current circuit are configured as a current mirror, having acurrent mirror multiple equal to a ratio of the first current and thesecond current; and the amplified current circuit is configured tosupply the second current from the power supply input to the regulatedvoltage output at the current mirror multiple when the first currentbetween the power supply input and the output transistor exceeds thethreshold current.

In another example embodiment, the amplifier control circuit includes aresistor for monitoring the first current between the power supply inputand the output transistor.

In another example embodiment, further comprising a differentialamplifier configured to compare a voltage reference with a feedbackvoltage received from the output; and wherein the output transistor iscoupled and controlled by the differential amplifier.

In another example embodiment, the voltage regulator is embedded in atleast one of: a wall charger, a wireless charger, a mobile phone, or aUSB connector, a notebook adapter, a TV adapter, or a PC adapter.

In another example embodiment, the current amplifier is part of anoutput stage of the voltage regulator.

In another example embodiment, the current amplifier is configured toreduce voltage steps and/or voltage spikes at the regulated voltageoutput.

In another example embodiment, the current amplifier includes a firstNMOS transistor configured to pass the first current and a second NMOStransistor configured to pass the second current; and the first andsecond NMOS transistors are configured as a current mirror.

In another example embodiment, the current amplifier is a first currentamplifier; further comprising a second current amplifier coupled betweenthe first current amplifier and the regulated voltage output; the secondcurrent amplifier is configured to supply a third current from the powersupply input to the regulated voltage output when the second currentbetween the power supply input and the first current amplifier exceeds asecond threshold current.

In another example embodiment, the first current amplifier includes afirst NMOS transistor configured to pass the first current and a secondNMOS transistor configured to pass the second current; the first andsecond NMOS transistors are configured as a first current mirror; thesecond current amplifier includes a first PMOS transistor configured topass the second current and a second PMOS transistor configured to passthe third current; and the first and second PMOS transistors areconfigured as a second current mirror.

According to an example embodiment, a voltage regulator, comprising: apower supply input; a regulated voltage output; an output transistorcoupled to the power supply input and the regulated voltage output; andmeans for current amplification coupled between the power supply inputand the regulated voltage output; wherein the means for currentamplification is configured to supply a second current from the powersupply input to the regulated voltage output when a first currentbetween the power supply input and the output transistor exceeds athreshold current.

According to an example embodiment, a method for voltage regulation in adevice having a power supply input, a regulated voltage output, and anoutput transistor coupled to the power supply input and the regulatedvoltage output, comprising: supplying a second current from the powersupply input to the regulated voltage output when a first currentbetween the power supply input and the output transistor exceeds athreshold current.

The above discussion is not intended to represent every exampleembodiment or every implementation within the scope of the current orfuture Claim sets. The Figures and Detailed Description that follow alsoexemplify various example embodiments.

Various example embodiments may be more completely understood inconsideration of the following Detailed Description in connection withthe accompanying Drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a first example of a voltage regulator;

FIG. 1B is an example set of voltage and current waveforms from thefirst example voltage regulator;

FIG. 2A is a second example of a voltage regulator.

FIG. 2B is an example set of voltage and current waveforms from thesecond example voltage regulator;

FIG. 3 is a third example of a voltage regulator.

FIG. 4A is a fourth example of a voltage regulator.

FIG. 4B is an example voltage vs. current waveform from the fourthexample voltage regulator;

FIG. 5 is a fifth example of a voltage regulator.

FIG. 6 is a sixth example of a voltage regulator.

FIG. 7 is a seventh example of a voltage regulator.

While the disclosure is amenable to various modifications andalternative forms, specifics thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that other embodiments, beyond the particularembodiments described, are possible as well. All modifications,equivalents, and alternative embodiments falling within the spirit andscope of the appended claims are covered as well.

DETAILED DESCRIPTION

In order to supply internal circuits operating at different voltagesupplies in an integrated circuit voltage regulators are often needed.To reduce the number of pins and external components these voltageregulators should preferably have no external components. Additionaldemands on these voltage regulators are low-current consumption andfrequency stability over a large range of output current and capacitiveload. In addition fast reaction to load current variations is requiredto avoid voltage spikes that might influence the performance of thecircuit or cause reliability problems.

FIG. 1A is a first example 100 of a voltage regulator.

The first example 100 voltage regulator (e.g. an NMOS regulator) is aclosed-loop series regulator in which an NMOS device is used as outputtransistor 102 (i.e. a source follower). Some advantages of thisregulator 100 include: simple frequency stabilization, good lineregulation and low output impedance.

This example 100 regulator uses a resistive feedback (i.e. voltagedivider) 104 to compare a regulated output voltage 106 with a referencevoltage 108. A differential amplifier 110 and a compensating capacitor112 form a low-frequency, dominant pole. The output transistor 102 formsa second pole with a load's 114 output capacitance 116. This second poleis larger than the unity-gain bandwidth defined by the internal gainstage. When the unity-gain bandwidth is small, then there is frequencystability over a wide range of output currents 118 and output capacitors116.

Fast load current 118 variations in the NMOS voltage regulator 100however can cause voltage spikes at the voltage output 106 called loadsteps. If the output (i.e. load) capacitance 116 (Cload) is small in anintegrated regulator, the load steps may not be suppressed by the loadcapacitance 116. The amplitude of the regulated output voltage 106 spikemainly depends on the Ids-Vgs relation of the NMOS output transistor102. The duration of the voltage 106 spikes depends on the unity gainbandwidth of the regulator 100.

FIG. 1B is an example set of voltage 120 and current 122 waveforms fromthe first example voltage regulator 100.

Load steps might be either negative 124 or positive 126, 128 dependenton the polarity of the current variation. Negative voltage spikes 124might cause problems with performance of attached circuits. In case ofperipheral digital circuits it may reduce the speed of such circuits. Incase of analog circuits, crosstalk due to the voltage spikes 124, 126 orcurrent biasing might be a problem.

FIG. 2 is a second example 200 of a voltage regulator. The secondexample 200 voltage regulator (e.g. an NMOS regulator) is also aclosed-loop series regulator in which an NMOS device is used as outputtransistor 232. FIG. 2B is an example set of voltage 220 and current 222waveforms from the second example voltage regulator 200.

The second voltage regulator 200 includes: an intermediate transistor202, resistive feedback 204, gate voltage 205, regulated output voltage206, reference voltage 208, differential amplifier 210, compensatingcapacitor 212, a replica output regulator 230, and an output transistor232. The load 214 includes an output capacitance 216 and output current218.

Positive voltage spikes might be a problem if the maximum voltage ratingof attached circuit is violated; however, if the maximum voltage ratingis close to a typical voltage level, the replica-output regulator 230prevents such spikes. The replica output regulator 230 uses the gatevoltage 205 in the closed-loop portion of the voltage regulator 200 asan input voltage.

When the gate of the replica output regulator 230 transistor is held ata constant voltage, frequency stability requirements are minimized asare positive voltage spikes (see FIG. 2B) due to load current 222variations. The regulated output voltage waveform 220 will depend on theoutput current waveform 222 through the Ids-Vgs relation of the NMOSoutput transistor 232; however there is still a negative load step 224.

FIG. 3 is a third example 300 of a voltage regulator. The third voltageregulator 300 includes: an output transistor 302, resistive feedback304, a gate voltage 305, a regulated output voltage 306, a referencevoltage 308, a differential amplifier 310, and a fast control circuit320. The load 314 includes an output capacitance 316 and an outputcurrent 318.

The third voltage regulator 300 presents another approach towardovercoming voltage steps due to large load current variations using afast control circuit 320 which can be either a window comparator or afast control loop. Both methods control the gate of the NMOS outputtransistor.

The fast control circuit 320 controls the gate voltage 305 in responseto a step in the output current 318. The fast control circuit 320includes window comparators (not shown) for monitoring the regulatedoutput voltage 306. If the regulated output voltage 306 goes beyond acertain voltage range the gate voltage 305 of the output transistor 302is controlled by the window comparator such that the regulated outputvoltage 306 does not go out of a defined regulated voltage range.

In some embodiments however fast comparators are required which mayconsume a large current. Also there can be a risk of instability due toa high-gain of the window comparator. Implementing window comparators(i.e. the fast control circuit 320) in a replica output voltageregulator may be complicated since the gate voltage 305 is basicallyfixed.

FIG. 4A is a fourth example 400 of a voltage regulator. The fourthvoltage regulator 400 includes: an output transistor 402 (e.g. an NMOStransistor), a feedback path 404, a gate voltage 405 (i.e. a controlvoltage), a regulated output voltage 406, a load current 407, areference voltage 408, a voltage controller 410 (e.g. differentialamplifier), and a current amplifier 412. The current amplifier 412 ispart of an output stage of the voltage regulator, and includes anamplifier control circuit 414 and an amplified current circuit 416.Connected to the fourth voltage regulator 400 is a power supply 418 anda load 420.

The current amplifier 412 is coupled between a power supply input, whichis between the power supply 418 and the voltage regulator 400, and theregulated voltage output which is between the voltage regulator 400 andthe load 420.

The current amplifier 412 is configured to supply a second current fromthe power supply input to the regulated voltage output when a firstcurrent between the power supply input and the output transistor 402exceeds a threshold current.

In the embodiment shown in FIG. 4A the first current is passing throughthe amplifier control circuit 414 and the second current is passingthrough the amplified current circuit 416.

The amplifier control circuit 414, between the power supply input andthe output transistor, is configured to sense the first current betweenthe power supply input and the output transistor 402.

The amplified current circuit 416 coupled to the amplifier controlcircuit 414 and between the power supply input and the regulated voltageoutput, is configured to supply the second current from the power supplyinput to the regulated voltage output when the first current between thepower supply input and the output transistor exceeds the thresholdcurrent.

In an example embodiment, the second current supplied by the currentamplifier 412 to the regulated voltage output is a multiple of the firstcurrent between the power supply input and the output transistor 402.

In an example embodiment the amplifier control circuit 414 and theamplified current circuit 416 are configured as a current mirror, havinga current mirror multiple equal to a ratio of the first current and thesecond current. The amplified current circuit 416 is configured tosupply the second current from the power supply input to the regulatedvoltage output at the current mirror multiple when the first currentbetween the power supply input and the output transistor exceeds thethreshold current.

The voltage controller 410 (e.g. differential amplifier) is configuredto compare the voltage reference 408 with the feedback voltage 404received from the output transistor 402. The output transistor 402 iscoupled and controlled by the voltage controller 410.

FIG. 4B is an example regulated output voltage vs. load current graph422 from the fourth example voltage regulator. Shown in the graph 422:one axis corresponds to the regulated output voltage 406, another axiscorresponds to the load current 407.

An I-V (i.e. current-voltage) waveform without current amplification 424is shown along with an I-V waveform with current amplification 426. Acurrent amplification activation point 428 represents the thresholdcurrent where the load current 407 (e.g. Iload) equals the first currentbetween the power supply input and the output transistor 402 (e.g.Iref).

By using current amplification in the output stage, the voltageregulator 400 improves upon load current regulation, as shown in FIG.4B, thereby reducing voltage steps and/or spikes. The voltage regulator400 can be used in integrated circuits requiring integrated fast voltageregulators for digital and analog circuits, and can be embedded in: awall charger, a wireless charger, a mobile phone, or a USB connector.

Thus instead of voltage regulation by controlling the gate voltage 405of the output transistor 402, the output current is amplified using thecurrent amplifier 412 once the current to the output transistor 402exceeds the preselected threshold value. Since current mode circuitstypically have a high bandwidth, using the voltage regulator 400 theload current 407 control can be very fast, resulting in a fast reactionto load current 407 variations. For replica output voltage regulatorsthe voltage regulator 400 has an advantage that with a constant gatevoltage the load step can still be improved.

FIG. 5 is a fifth example 500 of a voltage regulator. The fifth voltageregulator 500 includes: an output transistor 502, feedback (not shown),a gate voltage 505 (e.g. control voltage), a regulated output voltage506, a load current 507, a reference voltage (not shown), a voltagecontroller (not shown), and a current amplifier 512. The currentamplifier 512 includes a reference current circuit 514 (e.g. R1) formonitoring a first current (i.e. reference current) (Iref).

The current amplifier 512 also includes a current mirror 516 whichmultiplies the output transistor 502 drain current by a preselectedcurrent multiplication value (i.e. K) once the output transistor's 502drain current meets and/or exceeds Iref. In this example embodiment, apower supply (not shown) and a load 520 are also connected to the fifthvoltage regulator 500.

The fifth voltage regulator 500 otherwise operates in a manner similarto that described in FIGS. 4A and 4B.

FIG. 6 is a sixth example 600 of a voltage regulator. The sixth voltageregulator 600 includes: an output transistor 602 (e.g. Mn), feedback(not shown), a gate voltage 605 (e.g. control voltage), a regulatedoutput voltage 606, a load current 607, a reference voltage (not shown),a voltage controller (not shown), and a current amplifier 612.

The current amplifier 612 includes an amplifier control circuit 614 andan amplified current circuit 616. The amplifier control circuit 614includes a first NMOS transistor 613 and a resistor 615 (i.e. a bypassresistor for monitoring the first current (i.e. reference current,Iref). The amplified current circuit 616 includes second NMOS transistor617, wherein the first NMOST 613 and second NMOST 617 are configured asa current mirror.

Connected to the voltage regulator 600 is a power supply 618 and a load620 having an output capacitance 622.

The resistor 615 (R1) is coupled between the drain and source of theNMOS transistor 613 and defines the threshold current (e.g. Iload=Iref)where current amplification begins (e.g. the current amplificationactivation point 428).

Resistor R1 also sets a minimum bandwidth of the current mirror. Thebandwidth of the current mirror in one example embodiment is larger thanthe bandwidth of a current loop formed by the output transistor 602(e.g. Mn) and the current mirror.

When the current through the NMOST 613 is equal to Vt/R1 (e.g.Iload=Iref) the current mirror begins operation and the current isamplified K times (e.g. a 1:K ratio). Vt is the threshold voltage of theNMOST 613. When Vgs (the voltage between the NMOST's 613 gate andsource) is smaller than Vt, the NMOST 613 does not conduct.

As discussed with respect to FIGS. 4A and 4B, when Iload=Iref theIload−Vout waveform is shifted thereby reducing voltage steps at theload 620 as Iload increases. The dominant pole is formed by the outputtransistor 602 and the load capacitor 622. This embodiment can be asfast as a single transistor yielding a highest possible bandwidth.

FIG. 7 is a seventh example 700 of a voltage regulator. The seventhvoltage regulator 700 includes: an output transistor 702 (e.g. Mn),feedback (not shown), a gate voltage 705 (e.g. control voltage), aregulated output voltage 706, a load current 707, a reference voltage(not shown), a voltage controller (not shown), a first current amplifier712 and a second current amplifier 724.

The first current amplifier 712 includes an amplifier control circuit(not shown) having a first NMOST 713 and a resistor 715 for monitoring afirst current (i.e. reference current, Iref). The first currentamplifier 712 also includes an amplified current circuit (not shown)having a second NMOST 717, wherein the first MOST 713 and second MOST717 are configured as a first current mirror.

The second current amplifier 724 includes an amplifier control circuit(not shown) having a first PMOST 726 and a resistor 728 for monitoring asecond current through the second NMOST 717. The second currentamplifier 724 also includes an amplified current circuit (not shown)having a second PMOST 730 wherein the first PMOST 726 and second PMOST730 are configured as a second current mirror.

Connected to the voltage regulator 700 is a power supply 718 and a load720 having an output capacitance 722.

The first current amplifier 712 is configured to supply a second currentfrom the power supply input when a first current between the powersupply input and the output transistor 702 exceeds a first thresholdcurrent. The second current amplifier 724 is configured to supply athird current from the power supply input to the regulated voltageoutput 706 when the second current between the power supply input andthe first current amplifier 712 exceeds a second threshold current.Together the first and second current amplifiers 712 and 714 furthermultiply the current sent to the load 720

The seventh example voltage regulator 700 thus includes multiple currentamplification stages. These multiple current amplification stages offerhigher current amplification gain and bandwidth as compared to thesingle NMOST current mirror of FIG. 6.

In this specification, example embodiments have been presented in termsof a selected set of details. However, a person of ordinary skill in theart would understand that many other example embodiments may bepracticed which include a different selected set of these details. It isintended that the following claims cover all possible exampleembodiments.

1. A voltage regulator, comprising: a power supply input; a regulatedvoltage output; an output transistor coupled to the power supply inputand the regulated voltage output; and a current amplifier coupledbetween the power supply input and the regulated voltage output; whereinthe current amplifier is configured to supply a second current from thepower supply input to the regulated voltage output when a first currentbetween the power supply input and the output transistor exceeds athreshold current; wherein the current amplifier includes an amplifiercontrol circuit; and wherein the amplifier control circuit, is coupledto the power supply input and a drain or a source of the outputtransistor, and is configured to sense the first current between thepower supply input and the output transistor.
 2. The regulator of claim1: wherein the output transistor is an NMOS transistor having a draincoupled to the power supply input and a source coupled to the regulatedvoltage output.
 3. The regulator of claim 1: wherein the second currentsupplied by the current amplifier to the regulated voltage output is amultiple of the first current between the power supply input and theoutput transistor.
 4. The regulator of claim 1: wherein the currentamplifier includes an amplified current circuit; and wherein theamplified current circuit, is coupled to the amplifier control circuit,and is coupled between the power supply input and the regulated voltageoutput, and is configured to supply the second current from the powersupply input to the regulated voltage output when the first currentbetween the power supply input and the output transistor exceeds thethreshold current.
 5. The regulator of claim 4: wherein the amplifiercontrol circuit and the amplified current circuit are configured as acurrent mirror, having a current mirror multiple equal to a ratio of thefirst current and the second current; and wherein the amplified currentcircuit is configured to supply the second current from the power supplyinput to the regulated voltage output at the current mirror multiplewhen the first current between the power supply input and the outputtransistor exceeds the threshold current.
 6. The regulator of claim 4:wherein the amplifier control circuit includes a resistor for monitoringthe first current between the power supply input and the outputtransistor.
 7. The regulator of claim 1: further comprising adifferential amplifier configured to compare a voltage reference with afeedback voltage received from the output; and wherein the outputtransistor is coupled and controlled by the differential amplifier. 8.The regulator of claim 1: wherein the voltage regulator is embedded inat least one of: a wall charger, a wireless charger, a mobile phone, ora USB connector, a notebook adapter, a TV adapter, or a PC adapter. 9.The regulator of claim 1: wherein the current amplifier is part of anoutput stage of the voltage regulator.
 10. The regulator of claim 1:wherein the current amplifier is configured to reduce voltage stepsand/or voltage spikes at the regulated voltage output.
 11. The regulatorof claim 1: wherein the current amplifier includes a first NMOStransistor configured to pass the first current and a second NMOStransistor configured to pass the second current; and wherein the firstand second NMOS transistors are configured as a current mirror.
 12. Theregulator of claim 1: wherein the current amplifier is a first currentamplifier; further comprising a second current amplifier coupled betweenthe first current amplifier and the regulated voltage output; andwherein the second current amplifier is configured to supply a thirdcurrent from the power supply input to the regulated voltage output whenthe second current between the power supply input and the first currentamplifier exceeds a second threshold current.
 13. The regulator of claim12: wherein the first current amplifier includes a first NMOS transistorconfigured to pass the first current and a second NMOS transistorconfigured to pass the second current; wherein the first and second NMOStransistors are configured as a first current mirror; wherein the secondcurrent amplifier includes a first PMOS transistor configured to passthe second current and a second PMOS transistor configured to pass thethird current; and wherein the first and second PMOS transistors areconfigured as a second current mirror.
 14. A voltage regulator,comprising: a power supply input; a regulated voltage output; an outputtransistor coupled to the power supply input and the regulated voltageoutput; and means for current amplification coupled between the powersupply input and the regulated voltage output; wherein the means forcurrent amplification is configured to supply a second current from thepower supply input to the regulated voltage output when a first currentbetween the power supply input and the output transistor exceeds athreshold current; wherein the means for current amplification includesan amplifier control circuit; and wherein the amplifier control circuit,is coupled to the power supply input and a drain or a source of theoutput transistor, and is configured to sense the first current betweenthe power supply input and the output transistor.
 15. A method forvoltage regulation in a device having a power supply input, a regulatedvoltage output, an output transistor coupled to the power supply inputand the regulated voltage output and an amplifier control circuitcoupled to the power supply input and a drain or a source of the outputtransistor, comprising: supplying a second current from the power supplyinput to the regulated voltage output when a first current between thepower supply input and the output transistor exceeds a thresholdcurrent; and sensing the first current, with the amplifier controlcircuit, between the power supply input and the output transistor.
 16. Avoltage regulator, comprising: a power supply input; a regulated voltageoutput; an output transistor coupled to the power supply input and theregulated voltage output; and a current amplifier coupled between thepower supply input and the regulated voltage output; wherein the currentamplifier is configured to supply a second current from the power supplyinput to the regulated voltage output when a first current between thepower supply input and the output transistor exceeds a thresholdcurrent; wherein the current amplifier is a first current amplifier;further comprising a second current amplifier coupled between the firstcurrent amplifier and the regulated voltage output; and wherein thesecond current amplifier is configured to supply a third current fromthe power supply input to the regulated voltage output when the secondcurrent between the power supply input and the first current amplifierexceeds a second threshold current; wherein the first current amplifierincludes a first NMOS transistor configured to pass the first currentand a second NMOS transistor configured to pass the second current;wherein the first and second NMOS transistors are configured as a firstcurrent mirror; wherein the second current amplifier includes a firstPMOS transistor configured to pass the second current and a second PMOStransistor configured to pass the third current; and wherein the firstand second PMOS transistors are configured as a second current mirror.